The present invention relates to an operation-dependent advance supply of jet pumps, for example in a consumption-controlled fuel pump.
German patent document DE 42 24 981 A1 discloses a device for feeding fuel from a supply tank to an internal combustion engine of a motor vehicle. The fuel feeding device includes a supply tank at a suction side and a feeding aggregate at a pressure side connected to the internal combustion engine, as well as a branch conduit connected with the pressure side of the feeding system. It has a portion extended near the tank bottom, in which a jet pump is arranged. Its pressure pipe opens into a chamber which is separated from the tank chamber from which the feeding aggregate takes the fuel. A reliable, fast start of the internal combustion engine is guaranteed when in the branch conduit, as seen in the flow direction of the fuel, before the jet pump a check valve is arranged, which opens in response to exceeding of a predetermined limiting pressure in the branching conduit.
In mostly used embodiments, as a rule one of several jet pumps are used for cup filling of a fuel feeding aggregate or for circulating of fuel in the embodiment of a saddle tank from the pressure regulator. In the embodiment without the pressure regulator, the feeding of the jet pump or the jet pumps is performed from the advance. For this purpose in the fuel systems with the consumption-controlled fuel feeding (without a mechanical pressure regulator) in the advance mechanical overflow valves are utilized. It is open in the operation and releases a throttle cross-section which guarantees a predetermined return quantity. In the switching off case the mechanical overflow valve closes for maintaining the pressure in the fuel system.
By means of the mechanical overflow valve, the building of overpressure in fuel systems, for example in the case of thrust switching off or in the case of heat expansion of fuel is prevented, and a base load for the fuel feeding aggregate is produced, for improving this dynamic condition or in other words for shortening the response time. The return quantity can be used for supplying eventually available further jet pump. The mechanical overflow valves are formed so that the opening pressure and the throttle cross-section with the lowest fuel feeding pressure guarantees the return quantity required for the reliable operation of the jet pumps. Perjet pump the quantity is required of substantially 20 l/n.
In a consumption controlled fuel feeding aggregate, the system pressure is however variable, so that for example during cold or hot start or during hot operation the fuel quantity which flows back through the throttle increases. In particular during the start of the pressure build up starting from the opening pressure of the mechanical overflow valve, the lowest system pressure which takes place during the operation is made difficult by the flowing out fuel quantity. During turning off the pressure is held close blow the lowest system pressure, which makes difficult the pressure build up during the start by the overflow.
In the embodiment with advance supplied jet pumps, which are produced without a mechanical overflow valve but which are formed with a throttle, the pressure buildup depending on the flowing out of fuel is more difficult from the ambient pressure. During the cold start, where the effects of lower battery voltage and higher peak quantities meet with one another there is a great problem which has to be eliminated.
In accordance with the present invention a fuel supply system for supplying an internal combustion is provided, in which an advance supplied return is blockable by means of a switchable adjusting member and the return quantity is adjustable by means of a throttle element at all operational pressures above a minimal consumption.
With a switchable adjusting valve, instead of mechanical overflow valve, it is possible to completely block the return conduit during the starting phase so that the pressure build up for the high pressure part of the fuel supply system can be built by the fuel feeding aggregate without losses. In the turning off case an increased system pressure in the fuel supply system is maintained by means of the switchable adjusting member by locking the return conduit, so that during a hot start, by maintaining an increased system pressure, the vapor bubble formation in the fuel system can be suppressed.
The disadvantage of the mechanical overflow valve, that the pressure in the turning off case can be realized only close under the lowest system pressure and thereby this valve after exceeding of this pressure also opens and the pressure build up in the high pressure part is delayed, is eliminated in the inventive system.
In advantageous manner the switchable adjusting member can be connected with a control device which releases its control. The switchable adjusting member on the one hand can be formed as a blocking valve with a separate throttle part, and both components can be formed as an assembly, which is space-saving. With a fixedly predetermined throttle cross-section this can be designed with advantageous manner so that with lowest system operational pressure it guarantees a supply of the pump associated with return conduit for filling of the fuel feeding aggregate. In the embodiment with the switchable adjusting member as a cycled valve with each differently strong throttling after control, the overflow quantity can be adjusted in a desired manner and thereby can be adjusted optimally to the minimal pump consumption of such pumps, which are used for a cup filling of the fuel feeding aggregate.
In consumption-control electric fuel pumps with a variable fuel pressure a cycled valve can be used as a switchable adjusting member.
In accordance with another feature of the present invention a method or operation of the fuel supply system is provided, in which the obtained pressure build up is performed in accordance with the motor data with the control device.
By means of the inventive method for operation of a fuel supply system with the advance supplied return conduit, the blocking of the return conduit can be realized both during start and during turning off. Limiting of the overflow quantity at increased fuel pressure by reducing the throttle cross-section guarantees a reliable maximum motor consumption also at increased system pressure.
In advantageous manner the time point of opening of the return conduit by the switchable adjusting member can be activated after recognition of the start end, when the motor starts running. The start end can be defined advantageously for example by the setting of a corresponding bits. The time point of the opening of the switchable adjusting member can be advantageously realized for example by elapsing of a preselected time period, which for example is dependent on the battery voltage. The time period with which a timer is preadjusted, can be also dependent on nominal fuel pressure. In advantageous manner by means of pressure sensors in high pressure part of the fuel supply system and in fuel feeding module, the reaching of the fuel nominal pressure can be detected.
In another embodiment with the cycled valve, the overflow quantity for all operational pressure in the fuel supply system can be determined also by the minimal consumption for the pump for filling the fuel feeding aggregate.
The required ratio can be determined for example from a characteristic field in dependence on the fuel nominal pressure and the required minimal overflow quantity. The required overflow quantity can be selected constant or can be selected on a filling level in the cup of a fuel feeding aggregate, and with subdivided tank with several chambers it can be selected in dependence on the filling level in the tank chambers.
The novel features which are considered as characteristic for the present invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.